Semiconducitive catechol group encapsulant adhesion promoter for a packaged electronic device

ABSTRACT

A packaged electronic device includes a package substrate, an electronic component die mounted to the package substrate, and an encapsulant bonded to a portion of the package substrate at a catechol group adhesion promoted interface that includes benzene rings bonded with the package substrate and the encapsulant.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates in general to packaged electronic devices, and inparticular, to catechol group adhesion promoters for packaged electronicdevices.

Description of the Related Art

A packaged electronic device typically includes a semiconductor die orother electronic component that is attached to a package substrate andencapsulated with an encapsulant to provide protection to the electroniccomponent, e.g. during usage in an electronic system.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1 is a partial cross-sectional side view of a packaged electronicdevice according to one embodiment of the present invention.

FIG. 2 is a partial cross-sectional side view of a packaged electronicdevice according to another embodiment of the present invention.

FIG. 3 is a flow chart for forming a packaged electronic deviceaccording to one embodiment of the present invention.

FIG. 4 is a flow chart for forming a packaged electronic deviceaccording to another embodiment of the present invention.

FIG. 5 is sets forth molecular models of catechol group moleculesaccording to one embodiment of the present invention.

FIG. 6 is a molecular model showing a molecular structure of anencapsulant, adhesion promoter, and substrate structure prior to achemical reaction according to one embodiment of the present invention.

FIG. 7 is a molecular diagram model showing a molecular structure of anencapsulant, adhesion promoter, and substrate structure after a chemicalreaction according to one embodiment of the present invention.

The use of the same reference symbols in different drawings indicatesidentical items unless otherwise noted. The Figures are not necessarilydrawn to scale.

DETAILED DESCRIPTION

The following sets forth a detailed description of a mode for carryingout the invention. The description is intended to be illustrative of theinvention and should not be taken to be limiting.

In some environments such as automotive or industrial environments,encapsulant adhesion to a package substrate (e.g. a lead frame) can bechallenging. High shear stress, degradation of adhesion strength due tomoisture absorption and high temperatures, and variation in lead framefinishes can contribute to compromised adhesion between the packagesubstrate and the encapsulant.

As described below, a catechol group adhesion promoter is used forpromoting adhesion between an encapsulant and a package substrate in apackaged electronic device. In some examples, the applied adhesionpromoter molecules form bonds with molecules of the encapsulant andmolecules of the substrate to improve adhesion of the encapsulant to thesubstrate.

FIG. 1 is a cross-sectional side view of a packaged electronic device101 according to one embodiment of the present invention. Device 101includes a package substrate 103 and a die 105 attached to substrate 103with die adhesive 107. In the embodiment shown, the package substrateincludes a dielectric carrier 104 with conductive structures (e.g. bondpads 119) located thereon and conductive layers and vias (not shown)located therein. In other embodiments, a package substrate may be a leadframe (either a leaded or leadless) which is made of a metal material(e.g. copper). Still in other embodiment, a package substrate may haveother structures and/or be made of other materials.

In the embodiment shown, die 105 is a segment of a semiconductor waferthat has been processed with dielectric, semiconductive, and conductivematerials to form circuitry. In one embodiment, die 105 includes digitalcircuitry such as a processor, but may include other types of circuitrysuch as e.g. analog circuitry, memory, and/or logic gates. In someembodiments, the wafer may be made of silicon, silicon germanium, aIII-V semiconductor material, or other types of semiconductor material.In other embodiments, other types of electronic components (e.g. standalone capacitors, transistors, and inductors) may be encapsulated in apackaged electronic device. In one embodiment, a packaged electronicdevice may include multiple electronic components such as multiple dieor a die and a capacitor.

Die 105 and substrate 103 are encapsulated with encapsulant 109. In oneembodiment, encapsulant 109 is an epoxy mold compound that includes e.g.bisphenol-a or phenolic resin. In other embodiments other types ofencapsulants may be used, e.g. such as anhydride, novolac, phenolic, andunsaturated polyester.

In the embodiment shown, conductive structures (not shown) of die 105are coupled with wires 111 to conductive structures (e.g. pads 119) ofsubstrate 103. These wires are attached to conductive structures of die105 and substrate 103 by a wire bonding process. In other embodiments,die 105 may be electrically coupled to substrate 103 in other ways, e.g.with conductive traces. Die 105 may also be attached to substrate 103 inan upside down configuration wherein the conductive structures of thedie are attached to conductive structures of the substrate such as in aflip chip configuration.

Device 101 includes solder balls 113 for external electrical coupling toother devices in an electronic system. Solder balls 113 are electricallycoupled to pads 119 by conductive layers and vias (not shown) locatedwithin carrier 104. In other embodiments, device 101 may include othertypes of external conductors such as leads or pads.

In the embodiment shown, the packaged electronic device is a ball gridarray package. However in other embodiments, device 101 may be ofanother electronic packaging configuration type such as e.g. a QFNconfiguration type, a leaded configuration type (e.g. through hole orsurface mount), a QFP configuration type, or an SoIC configuration type.

Device 101 includes a catechol group adhesion promoted interface 121. Acatechol group adhesion promoted interface is an interface between twostructures that is formed from the application of a catechol groupadhesion promoter applied between the two structures for forming bondsbetween the two structures. In the embodiment shown, interface 121 isformed by the application of a layer of a catechol group adhesionpromoter applied between substrate 103 and encapsulant 109 for formingchemical bonds between encapsulant 109 and substrate 103, and also forforming chemical bonds between substrate 103 and die adhesive 107.Interface 121 includes molecules with benzene rings formed from areaction of the promoter and substrate molecules and the promoter andencapsulant molecules.

A catechol group adhesion promoter is an adhesion promoter that includescatechol molecules and/or catechol derivative molecules. Catechol isalso known as 1,2, dihydroxybenzene or pyrocatechol. A catecholderivative is a substance having a molecule that includes a benzene ringand at least two hydroxyl groups bonded to the ring.

FIG. 5 sets forth molecular models of catechol and various catecholderivatives. Model 501 is a model of a catechol molecule. Models fordopamine, alpha-methyldopamine, norepinephrine, dihydroxyphenylalanine(DOPA), alpha-methyldopa, droxidopa, and 5-hydroxydopamine molecules arealso shown in FIG. 5. In the dopamine molecule shown in FIG. 5, box 503is drawn around the benzene ring and two hydroxyls (“HO”) bonded to thering.

Referring back to FIG. 1, interface 121 is shown as being located onsubstrate 103. Interface 121 includes one or more layers of moleculesthat are bonded to molecules of the structures on either side of theinterface. In the embodiment of FIG. 1, the adhesion promoter is appliedto substrate 103 prior to the attachment of die 105. Consequentlyinterface 121 is shown as being located beneath adhesive 107. Thechemical makeup of interface 121 at a particular location is dependenton the materials on either side of interface 121. For example, thechemical makeup of interface 121 beneath adhesive 107 may be differentthan that between encapsulant 109 and substrate 103. Furthermore, wheresubstrate 103 has multiple materials at its top surface (e.g. bothdielectric and metal), the chemical makeup of interface 121 would bedifferent at different locations as well. In some embodiments, interface121 may also include unreacted catechol group molecules.

In the embodiment of FIG. 1, the adhesion promoter interface is notlocated on the wire bonds of pads 119. This is due in some embodiment tothe pads being scrubbed prior to wirebonding which removes the interfacemolecules.

In FIG. 1, interface 121 is shown as being thicker than it actually isrelative to other structures of device 101. This is done in the figuresto illustrate the location of interface 121. In some embodiments,interface 121 may only be one molecule thick or a few molecules thick.

In one embodiment, the adhesion promoter includes other substances inaddition to the catechol group molecules. For example, the promoter mayinclude a fluorinated copolymer that aids in the adhesion reaction withsome materials such as metals (e.g. copper). The promoter may includesodium bisulfate.

In one embodiment, the substances (including the promoter) are dissolvedin an aqueous buffer solution such as an aqueous hydrochloride for itsapplication to the substrate. In another embodiment, the substances(including the promoter are dissolved in ethanol. In one embodiment, thepromoter is applied to substrate 103 by immersing the substrate in thepromoter solution. In one embodiment, the solution is heated during theimmersion process. During the immersion process, the promoter reactswith the surface of the substrate to form chemical bonds between thebenzene rings of the promoter and molecules of the substrate. Theresultant molecules may also have a free hydroxyl that will aid insubsequent bonding to the encapsulant. Because the entire panel isimmersed in some embodiments, substrate 103 includes a layer 122 ofmaterial that includes molecules with benzene rings on the bottom of thesubstrate 103. In one embodiment, the material formed from the reactionof the adhesion promoter with the surfaces of the substrate ischaracterized as a self assembled monolayer, which is molecular assemblyformed spontaneously on a surface by adsorption.

In the embodiment shown, substrate 103 was part of a panel of packagedsubstrates when immersed. After die attachment, wirebonding, andencapsulation, the panel is separated into multiple packages. Thus, inthe embodiment shown, no adhesion promoter material is located on theside of device 101.

FIGS. 6 and 7 show molecular models illustrating the molecules of thepromoter, substrate, and encapsulant and their reaction to each other.

FIG. 6 shows a model for a catechol molecule 603 in proximity to a modelfor encapsulant molecule 601 and in proximity to a model for a metalmolecule 619 of a substrate. In some embodiments, this state of themolecules may not actually exist in that the adhesion promoter firstbonds to the substrate material during its application and then bonds tothe encapsulant during the encapsulation process. However, FIG. 6 isbeing shown to illustrate the chemical processes involved in thechemical bonding.

The encapsulant molecule 601 includes nitrogen, CH, CH₂, and hydroxyls(e.g. hydroxyl 609). The “R” of molecule 601 represents any chemicalmolecule of the encapsulant material. The complete structure of molecule601 is not shown in FIG. 6 in that CH, CH₂, and hydroxyls are locatedabove the top nitrogen element in FIG. 6. The “M” in molecule 619represents any metal molecule (e.g. copper). Molecule 619 includes ahydroxyl 615. Catechol molecule 603 includes benzene ring 605 andhydroxyls 607 and 613.

FIG. 7 shows a model of a molecule 700 of a catechol adhesion promotedinterface wherein the catechol molecule 603 has reacted with metalmolecule 619 and reacted with encapsulant molecule 601 to form aresultant molecule 700. In forming molecule 700, metal molecule 619 ischemically bonded to benzene ring 605 with an oxygen chemical covalentbond 705 and encapsulant molecule 601 is bonded to ring 605 with anoxygen chemical covalent bond 701. During the chemical reactions,hydroxyl 615 of metal molecule 619 reacts with hydroxyl 613 of catecholmolecule 603 to form oxygen bond 705 and a water molecule. Also duringthe reactions, hydroxyl 609 reacts with hydroxyl 607 to form oxygen bond701 and a water molecule. Resultant molecule 700 includes material froman encapsulant molecule 601, an adhesion promoter molecule 603, and asubstrate molecule 619. Accordingly, the resultant molecules provide fora stronger bond between the encapsulant and the substrate. During theencapsulation process, the water molecules are removed by out gassing.

In some embodiments, not all of the catechol group molecules of acatechol group adhesion promoter chemically bond to both the substratemolecules and the encapsulant molecules. For example, in FIG. 7, benzenering 707 is only chemically bonded to material of the encapsulant layerand not material of the substrate. In other embodiments, some benzenerings of an interface would only be chemically bonded to molecules ofthe substrate. Still in other embodiments, the interface would includecatechol group molecules that are unreacted with either encapsulantmolecules or substrate molecules.

In other embodiment, the molecules may be bonded together by other typesof chemical bonds other than the oxygen covalent bonds shown in FIG. 7.For example, the benzene ring may be bonded to either molecules of theencapsulant or molecules of the substrate with a hydrogen or ionic bond.In other embodiments, the benzene rings of an interface layer maybeinterconnected with each other with carbon bonds to form a honeycomblike structure. In one embodiment, the resultant molecules of theinterface form a self assembled monolayer.

FIG. 2 is a cross sectional side view of a packaged electronic deviceaccording to another embodiment of the present invention. Packageddevice 201 is similar to packaged device 101 except that the adhesionpromoter is applied after wiring bonding with the embodiment of FIG. 2.Otherwise, substrate 203, adhesive 207, die 205, encapsulant 209, pads219, wires 211, and solder balls 213 are similar to substrate 103,adhesive 107, die 105, encapsulant 109, pads 119, wires 111, and solderballs 113 of FIG. 1.

In the embodiment of FIG. 2, because the adhesion promoter is applied tosubstrate 203 after the attachment of die 205 and after wire bonding,the adhesion promoter is applied to the surfaces of die 205 and wires211. Accordingly, interface 221 is located at the surfaces of the wiresand dies 205 where the encapsulant chemically bonds with the metal ofwires 211 and the surface of die 205. Also, material 222 is formed bythe application of catechol group adhesion promoter to the bottom ofsubstrate 203.

FIG. 3 sets forth a flow diagram 301 for making a packaged electronicdevice similar to device 101. In process 303, an adhesion promoter isapplied to a substrate panel. In one embodiment, the adhesion promoteris applied by immersing a multi substrate panel in a liquid containingthe catechol group molecules. In one embodiment, the liquid is at atemperature in the range of 70-120 Celsius when the panel is immersed inthe liquid, but the liquid may be at other temperatures in otherembodiments. During the immersion, the benzene rings of the catecholgroup molecules react with the molecules of the substrate to chemicallybond to the material of the substrate. However, the promoter may beapplied by other methods. In some embodiment, the solution is alkalinewith a PH of 6 to 9. In other embodiments, the solution may be slightlyacidic with a PH of 3 to 6. In some embodiments where each substrate hasmultiple structures made of different materials at its surface, thesubstrate may be dipped in multiple solutions of different PH levels, ofdifferent catechol group molecules, and/or of other different substancesso that the benzene rings chemically bond effectively to the differentmaterials of the substrate.

In process 305, the die (or other electronic component) is attached tothe substrate. In process 307, the die is electrically coupled to thesubstrate (e.g. by wirebonding). In some embodiments such as with someflip chip configurations, processes 305 and 307 are performed at thesame time where the die is electrically coupled when attached to thesubstrate.

In process 309, the substrate and die are encapsulated with anencapsulant. In one embodiment, the encapsulant is applied by a transfermolding process. However, in other embodiments, the encapsulant may beformed by other encapsulating processes e.g. by a compression moldingprocess. The encapsulation process typically includes the application ofheat to the encapsulating assembly. During the encapsulating process,the encapsulant molecules chemically react with the catechol adhesionpromoter bonded to the substrate surface to form chemical bonds. As aresult, the encapsulant is chemically bonded to material of thesubstrate with the benzene rings of the catechol adhesion promotedinterface.

After the encapsulating process, the encapsulated substrate panel issingulated into multiple packaged devices, e.g. with a saw or laser. Insome embodiments, solder balls maybe added to the panel beforesingulation.

FIG. 4 sets forth a flow diagram 401 for making a packaged electronicdevice similar to device 201. The processes of FIG. 4 is similar to theprocesses of FIG. 3 except that the catechol group adhesion promoter isapplied to the substrate (in process 407) after the attachment of thedie to the substrate (in process 403) and the attachment of wire bonds(in process 405). Accordingly, the material formed by the application ofthe adhesion promoter is attached to the wire bonds and die as well asto exposed surfaces of the substrate. Processes 409 and 411 are similarto processes 309 and 311 in the embodiment of FIG. 3.

In other embodiments, the catechol group adhesion promoter is appliedafter attachment of the die to the substrate (process 403) but beforewire bonding (process 405).

In one embodiment, applying a catechol group adhesion promoter to asurface of a substrate prior to encapsulation of the surface of thesubstrate acts to increase the bond strength between the surface of thesubstrate and the encapsulant. The catechol group adhesion promoter actsto form molecules each with a benzene ring that is chemically bonded tomaterial of the encapsulant and to material of the substrate. This maybe especially important for substrates having an encapsulating surfacethat is metal (e.g. copper, silver plated copper, nickel palladium gold,gold palladium, or gold). Without the adhesion promoter, it may bedifficult to form chemical bonds between the encapsulant and metal.

The chemical bonds formed by the use of the adhesion promoter increasethe bond strength between the encapsulant and substrate. Providingincreased bond strength between the encapsulant and substrate may enablea higher reliability of the package which is important in hightemperature, high humidity applications such as in automotive orindustrial applications. In some embodiments, the encapsulant remainsbonded to the substrate at temperatures ranging from −80 to 300 degreesCelsius.

With applying the promoter to the substrate, the ingredients of thepromoter can be tailored to the surface materials of the substrate toincrease the bond strength between the benzene rings and the substrate.Also, by applying the adhesion promoter to the surface of the substrate,the surface can be more consistently coated with molecules having freehydroxyls, which provide for a better surface for subsequentencapsulation.

In one embodiment, a method comprises attaching an electronic componentto a package substrate and encapsulating a surface of the packagesubstrate with an encapsulant. Prior to the encapsulating, an adhesionpromoter is applied to the surface. The adhesion promoter includescatechol group molecules.

In another embodiment, a packaged electronic device includes a packagesubstrate, an electronic component attached to the package substrate,and an encapsulant bonded to a portion of the package substrate at acatechol group adhesion promoted interface that includes a plurality ofbenzene rings bonded with the package substrate and the encapsulant.

In another embodiment, a packaged electronic device includes a packagesubstrate including a surface, an encapsulant encapsulating the surface,and a self assembled monolayer interface between the surface and theencapsulant. The self assembled monolayer interface including aplurality of molecules each including a benzene ring chemically bondedto the surface and to the encapsulant.

While particular embodiments of the present invention have been shownand described, it will be recognized to those skilled in the art that,based upon the teachings herein, further changes and modifications maybe made without departing from this invention and its broader aspects,and thus, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention.

1. A method comprising: attaching an electronic component to a packagesubstrate; encapsulating a surface of the package substrate with anencapsulant, wherein prior to the encapsulating, an adhesion promoter isapplied to the surface, wherein the adhesion promoter includes catecholgroup molecules.
 2. The method of claim 1, wherein the catechol groupmolecules include molecules of at least one of a group consisting ofdihydroxybenzene, dopamine, alpha-methyldopamine, norepinephrine,dihydroxyphenylalanine, alpha-methyldopa, droxidopa, and5-hydroxydopamine.
 3. The method of claim 1, wherein as a result of theadhesion promoter being applied to the surface, chemical bonds betweenbenzene rings of the catechol group molecules and the package substrateare formed.
 4. The method of claim 1, wherein the electronic componentis attached prior to the adhesion promoter being applied to the surface.5. The method of claim 1, wherein the electronic component is attachedafter to the adhesion promoter is applied to the surface.
 6. The methodof claim 1 further comprising: electrically coupling the electroniccomponent to the package substrate prior to the adhesion promoter beingapplied to the surface.
 7. The method of claim 1, wherein as a result ofthe encapsulating, benzene rings of at least some of the catechol groupmolecules are chemically bonded to both the package substrate and to theencapsulant.
 8. The method of claim 1 wherein as a result of theencapsulating, benzene rings of at least some of the catechol groupmolecules are chemically bonded to both the package substrate and to theencapsulant.
 9. The method of claim 1 wherein the surface ischaracterized as a surface of a metal of the package substrate. 10-20.(canceled)
 21. A method comprising: providing a package substrate;applying a catechol group adhesion promoter to the package substrate;attaching an electronic component to the package substrate; forming afirst catechol group adhesion promoted interface between the electroniccomponent and the package substrate; and bonding an encapsulant to aportion of the package substrate at a second catechol group adhesionpromoted interface formed between the package substrate and theencapsulant.
 22. The method of claim 21, wherein forming the adhesionpromoted interfaces includes chemically bonding a plurality of benzenerings to a surface of the package substrate.
 23. The method of claim 22,wherein at least some of the plurality of benzene rings are chemicallybonded to the encapsulant.
 24. The method of claim 21, furthercomprising: forming a catechol group molecule between the encapsulantand the package substrate.
 25. The method of claim 24, wherein thecatechol group molecule is characterized as one of a group consisting ofdihydroxybenzene, dopamine, alpha-methyldopamine, norepinephrine,dihydroxyphenylalanine, alpha-methyldopa, droxidopa, and5-hydroxydopamine.
 26. The method of claim 21, wherein the encapsulantremains bonded to the package substrate at temperatures ranging between−80 degrees Celsius and 300 degrees Celsius.
 27. The method of claim 21,wherein the second catechol group adhesion promoted interface is locatedat a metal surface of the package substrate.
 28. The method of claim 21,further comprising: electrically coupling the electronic component andthe package substrate with a plurality of wire bonds, wherein theencapsulant is located on surfaces of the plurality of wire bonds. 29.The method of claim 21, wherein the first and second catechol groupadhesion promoted interfaces are characterized as a self assembledmonolayer interface.
 30. A method comprising: providing a packagesubstrate including a surface; attaching an electronic device to aportion of the surface; encapsulating the surface with an encapsulant;forming a self assembled monolayer interface between the surface and theencapsulant and between the portion of the surface and the electronicdevice, the self assembled monolayer interface including a plurality ofmolecules each including a benzene ring chemically bonded to the surfaceand to the encapsulant.
 31. The method of claim 30, wherein the surfaceis characterized as a metal.